Last year, the Mississippi woman became the first American to give up a tooth for an eye.

Dr. Victor Perez at the University of Miami's Bascom Palmer Eye Institute extracted Thornton's tooth, put it in her eye and used the tooth to anchor a prosthetic lens, which gave her back her vision.

She couldn't believe what she saw later.

In a denial letter from Humana Insurance, the company wrote "medical records did not show that the eye surgery....was medically necessary and reasonable."

When the TODAY show contacted Humana to ask them how it was possible that giving a blind person their sight back was not medically necessary and reasonable, they said they'd investigate.

Humana later said, in part, it "...will pay the outstanding physician claim."

But without a standard among insurance companies, Thornton worries that other patients waiting for this unique surgery may also be refused coverage.

"They can't do it," she said. "They can't afford to do it and if they have insurance [companies] that are saying 'This is cosmetic surgery or experimental surgery and we're not going to pay for it,' they're not going to have it done. They will stay blind for the rest of their lives."

Thornton said she thought she would never see again. She lost her sight, hair, nails and much of her skin when she developed a severe skin disorder called Stevens-Johnson syndrome in 2000.